In manufacturing electronic devices, plasma processing is performed on a substrate by using a plasma processing apparatus. The plasma processing apparatus includes a chamber and a supporting table. The supporting table is provided in the chamber. In the plasma processing apparatus, the substrate is disposed on the supporting table in a region surrounded by a focus ring. The focus ring is used to ensure in-plane uniformity of the plasma processing. Specifically, the focus ring is used to adjust a shape of a sheath such that ions in plasma are vertically incident on edge region of the substrate.
The focus ring is consumed by the plasma processing. As the focus ring is consumed by the plasma processing, the thickness of the focus ring decreases. The decrease in the thickness of the focus ring leads to changes in the shape of the sheath. Accordingly, an incident direction of ions in the plasma on the edge region of the substrate is inclined inwardly with respect to a vertical direction. As a result, the in-plane uniformity of the plasma processing deteriorates. Japanese Patent Application Publication No. 2007-258417 discloses that a negative DC voltage is applied to a focus ring to correct a shape of a sheath that has changed by the decrease in the thickness of the focus ring.
It is not necessarily preferable that ions are vertically incident on the edge region of the substrate. For example, when a mask provided on a film of a substrate provides an opening that is outwardly inclined with respect to the vertical direction in the edge region of the substrate, ions need to be incident on the edge region of the substrate in a direction inclined inwardly with respect to the vertical direction in order to form a vertically extending opening in the film in the edge region by plasma etching. In the opposite case, ions need to be incident on the edge region of the substrate in a direction inclined outwardly with respect to the vertical direction. Therefore, it is required to control the incident direction of the ions on the edge region of the substrate to a desired direction between the direction inclined inwardly with respect to the vertical direction and the direction inclined outwardly with respect to the vertical direction.